The present invention relates to a motor vehicle exhaust support hanger, in general, and more particularly to a support hanger or bracket for a catalytic converter, and to a method for salvaging catalytic converters.
Emission control systems for internal combustion engines, and more particularly for motor vehicle internal combustion engines, utilize a catalytic converter connected in the engine exhaust between the exhaust manifold and the muffler. Catalytic converters generally take the form of a gas expansion housing containing a metallic mesh and catalyst combination capable of exothermally reducing nitrogen oxides while oxidizing carbon monoxide and hydrocarbons present in the exhaust gases of the engine. The exothermic reaction generates considerable heat which subjects the converter housing to a succession of heating cycles while the engine is running, and cooling cycles while the engine is shut off. The housing of the catalytic converter is often formed of heavy gauge steel material, often a stainless steel, and it is sometimes provided with shallow embossed ribs to allow the housing to be subject to successive cycles of expansion and contraction without cracking.
Catalytic converters are supported from the frame of the motor vehicle, as close to the engine as feasible, in a substantially horizontal position below the frame, by means of a stamped bracket. The catalytic converter housing is made of two half shells welded together such as to form the full housing. Each half shell includes a half portion of an integrally formed inlet annular neck and outlet annular neck for connection, respectively, to the exhaust pipe and to a pipe connecting the catalytic converter to the muffler. The support bracket has mounting apertures for bolting to a frame member, and a circular aperture through which the exhaust tubular outlet collar is passed prior to flaring the rim of the tubular neck for junction to the complementarily flared end rim of the pipe. The bracket is welded to the outlet collar behind the flared-out portion of the collar. The flared collar is fastened to the complementarily flared end rim of the pipe by way of an appropriate flange mounted on the end of the pipe and having mounting apertures aligned with corresonding mounting apertures on the bracket for passage therethrough of bolts which, when tightened, provides a secure junction of the converter outlet collar and pipe inlet flared rim.
Such an installation for a catalytic converter placed in series in the exhaust system of a motor vehicle powered by an internal combustion engine is generally satisfactory when the motor vehicle is placed in service, and for a few years thereafter. However, progressive deterioration of the converter housing, of the support bracket itself, and more particularly of the weld fastening the support bracket to the converter housing outlet collar takes place after a period of time depending on the type of service imposed upon the vehicle, light duty or heavy duty, the frequency of the heating to cooling cycles to which the catalytic converter is subjected, and the ambient or surrounding in which the motor vehicle is operated. In time, fatigue, corrosion and oxidation which, apparently, is accelerated more particularly at the weld in view of the difference in the metallurgy of the bracket, the converter housing and the weld seam, cause the bracket and the converter outlet collar to become detached. This in turn causes gas leakage at the junction between the converter outlet flared collar and the pipe inlet flared rim, as the clamping bolts are no longer able to draw the pipe flange tightly towards the loose and relatively fragile and bendable bracket, in view of the excessive reduction in thickness of the bracket due to corrosion and, eventually, the combined effect of shock and vibrations may result in rupture of the bracket due to the reduction in strength of the fatigued and corroded metal of the bracket itself. The repair hitherto available when a catalytic converter support bracket fails is full replacement of the whole converter by a new one having an appropriate welded-on support bracket which, evidently, is a very costly operation in view of the high cost of catalytic converters.